1. Field of the Invention
This invention relates to an electrophotographic photosensitive member and an electrophotographic apparatus using the electrophotographic photosensitive member.
2. Description of the Prior Art
Conventionally, inorganic photoconductive materials, such as zinc oxide, selenium and cadmium sulfide, are known as photoconductive materials for use in electrophotographic photosensitive members. On the other hand, organic photoconductive materials, such as polyvinylcarbazole, phthalocyanine, and azo pigments, have attracted attention and found wide use because of their advantages in terms of high productivity and pollution-free properties, although they were previously unsatisfactory in terms of photoconductive characteristics and durability. Recently, organic photoconductive materials having improved photoconductive characteristics and durability have been proposed and the photoconductive characteristics of some of organic photoconductive materials presently developed are superior than those of inorganic photoconductive materials.
An electrophotographic photoconductive member must have durabilities with respect to various factors, because it repeatedly undergoes charging, exposure, development, transfer, cleaning and discharging in an electrophotography process in a laser beam printer or the like. In particular, resistance to mechanical action, such as wear resistance and scratch resistance, are the most determinative factors for extending the life of an electrophotographic photosensitive member.
Ordinarily, organic photoconductive materials such as those mentioned above are formed as a film by using a binder resin. Therefore, the wear resistance and scratch resistance of an electrophotographic photosensitive member using an organic photoconductive material are almost entirely determined by the selection of the binder resin. However, it is difficult to select a binder resin having substantially no influence upon the photoconductive characteristics of an organic photoconductive material. Therefore, the wear resistance of electrophotographic photosensitive members using organic photoconductive materials is far smaller than that of electrophotographic photosensitive members using inorganic photoconductive materials.
In an electrophotography process, a cleaning step is most influential in determining the wear resistance. With the recent changes in cleaning conditions, e.g., the reduction in developer particle size, there has arisen a need for an increase in the accuracy of cleaning operations. Also, with the progress of space saving designs, there has been a need for a simpler processing apparatus arrangement.
A cleaning method most suitably used to satisfy these needs is a blade cleaning method. Blade cleaning is performed by bringing a resilient member such as a plate-like polyurethane member against a surface of a photosensitive member. A large frictional force is thereby caused between the photoconductive member and the blade to wear down the surface of the photosensitive member. The life of the photosensitive member is thereby reduced. To cope with this problem, it is necessary to strengthen the photosensitive member.
The photosensitive member may be strengthened by using a high molecular weight binder resin or a curable binder resin. However, a high molecular weight binder resin acts to increase the viscosity of a coating material in a coating process, which is ordinarily used to manufacture organic photosensitive members. There is therefore a limitation upon increasing the molecular weight of the binder resin. A curable binder resin acts to reduce the reactivity of an organic photoconductive material at the time of curing, because impurities are formed by (1) unreacted functional groups, (2) a reaction product of a polymerization initiator or the like. Such impurities result in failure to obtain suitable photoconductive characteristics.